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</head><body><div id="web_bg"></div><div id="sidebar"><div id="menu-mask"></div><div id="sidebar-menus"><div class="author-avatar"><img class="avatar-img" data-lazy-src="https://qiniu.codekylin.cn/img/20200807181526.jpg" onerror="onerror=null;src='https://qiniu.codekylin.cn/github/img/friend_404.gif'" alt="avatar"/></div><div class="site-data"><div class="data-item is-center"><div class="data-item-link"><a href="/archives/"><div class="headline">文章</div><div class="length-num">362</div></a></div></div><div class="data-item is-center"><div class="data-item-link"><a href="/tags/"><div class="headline">标签</div><div class="length-num">427</div></a></div></div><div class="data-item is-center"><div class="data-item-link"><a href="/categories/"><div class="headline">分类</div><div class="length-num">101</div></a></div></div></div><hr/><div class="menus_items"><div class="menus_item"><a class="site-page" href="/"><i class="fa-fw fa fa-home"></i><span> 首页</span></a></div><div class="menus_item"><a class="site-page" href="/archives/"><i class="fa-fw fa fa-archive"></i><span> 时间轴</span></a></div><div class="menus_item"><a class="site-page" href="/tags/"><i class="fa-fw fa fa-tags"></i><span> 标签</span></a></div><div class="menus_item"><a class="site-page" href="/categories/"><i class="fa-fw fa fa-folder-open"></i><span> 分类</span></a></div><div class="menus_item"><a class="site-page" href="/link/"><i class="fa-fw fa fa-link"></i><span> 友链</span></a></div><div class="menus_item"><a class="site-page" href="/about/"><i class="fa-fw fa fa-heart"></i><span> 关于</span></a></div></div></div></div><div class="post" id="body-wrap"><header class="post-bg" id="page-header" style="background-image: url('https://qiniu.codekylin.cn/github/images/20200701211402.jpg')"><nav id="nav"><span id="blog_name"><a id="site-name" href="/">Kylin</a></span><div id="menus"><div id="search-button"><a class="site-page social-icon search"><i class="fas fa-search fa-fw"></i><span> 搜索</span></a></div><div class="menus_items"><div class="menus_item"><a class="site-page" href="/"><i class="fa-fw fa fa-home"></i><span> 首页</span></a></div><div class="menus_item"><a class="site-page" href="/archives/"><i class="fa-fw fa fa-archive"></i><span> 时间轴</span></a></div><div class="menus_item"><a class="site-page" href="/tags/"><i class="fa-fw fa fa-tags"></i><span> 标签</span></a></div><div class="menus_item"><a class="site-page" href="/categories/"><i class="fa-fw fa fa-folder-open"></i><span> 分类</span></a></div><div class="menus_item"><a class="site-page" href="/link/"><i class="fa-fw fa fa-link"></i><span> 友链</span></a></div><div class="menus_item"><a class="site-page" href="/about/"><i class="fa-fw fa fa-heart"></i><span> 关于</span></a></div></div><div id="toggle-menu"><a class="site-page"><i class="fas fa-bars fa-fw"></i></a></div></div></nav><div id="post-info"><h1 class="post-title">Netty编解码器和handler的调用机制</h1><div id="post-meta"><div class="meta-firstline"><span class="post-meta-date"><i class="far fa-calendar-alt fa-fw post-meta-icon"></i><span class="post-meta-label">发表于</span><time class="post-meta-date-created" datetime="2020-11-23T08:57:53.000Z" title="发表于 2020-11-23 16:57:53">2020-11-23</time><span class="post-meta-separator">|</span><i class="fas fa-history fa-fw post-meta-icon"></i><span class="post-meta-label">更新于</span><time class="post-meta-date-updated" datetime="2022-07-12T11:42:50.022Z" title="更新于 2022-07-12 19:42:50">2022-07-12</time></span><span class="post-meta-categories"><span class="post-meta-separator">|</span><i class="fas fa-inbox fa-fw post-meta-icon"></i><a class="post-meta-categories" href="/categories/Netty/">Netty</a></span></div><div class="meta-secondline"><span class="post-meta-separator">|</span><span class="post-meta-wordcount"><i class="far fa-file-word fa-fw post-meta-icon"></i><span class="post-meta-label">字数总计:</span><span class="word-count">2.2k</span><span class="post-meta-separator">|</span><i class="far fa-clock fa-fw post-meta-icon"></i><span class="post-meta-label">阅读时长:</span><span>8分钟</span></span></div></div></div></header><main class="layout" id="content-inner"><div id="post"><article class="post-content" id="article-container"><h2 id="handler基本说明"><a href="#handler基本说明" class="headerlink" title="handler基本说明"></a>handler基本说明</h2><p>Netty的主要组件有Channel、EventLoop、ChannelFuture、ChannelHandler、ChannelPipe等</p>
<p><mark>其中ChannelHandler充当了处理入站和出站数据的应用程序逻辑的容器。</mark></p>
<p>例如，实现ChannelInboundHandler接口（或ChannelInboundHandlerAdapter），你就可以接收入站事件和数据，这些数据会被业务逻辑处理。当要给客户端发送响应时，也可以从ChannelInboundHandler冲刷数据。业务逻辑通常写在一个或者多个ChannelInboundHandler中。ChannelOutboundHandler原理一样，只不过它是用来处理出站数据的。</p>
<p><mark>ChannelPipeline提供了ChannelHandler链的容器</mark></p>
<p>以客户端应用程序为例，如果事件的运动方向是从客户端到服务端的，那么我们称这些事件为出站的，即客户端发送给服务端的数据会通过pipeline中的一系列ChannelOutboundHandler，并被这些Handler处理，反之则称为入站的。同理，对于服务端来说，也是一样的，有数据来就是入站，有数据输出就是出站。</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123171017623.png" alt="image-20201123171017623"></p>
<blockquote>
<p>为什么服务端和客户端的handler都是继承SimpleChannelInboundHandler，而没有ChannelOutboundHandler出站类？</p>
</blockquote>
<p>实际上当我们在handler中调用ctx.writeAndFlush()方法后，就会将数据交给ChannelOutboundHandler进行出站处理，只是我们没有去定义出站类而已，若有需求可以自己去实现ChannelOutboundHandler出站类。</p>
<p>总结就是客户端和服务端都有出站和入站的操作，形成一个循环链</p>
<p><code>服务端--------&gt;出站--------&gt;入站--------&gt;客户端 --------&gt;出站--------&gt;入站--------&gt;服务端</code></p>
<h2 id="编解码器"><a href="#编解码器" class="headerlink" title="编解码器"></a>编解码器</h2><p>当Netty发送或者接受一个消息的时候，就将会发生一次数据转换。<mark>入站消息会被解码：从字节转换为另一种格式（比如java对象）；如果是出站消息，它会被编码成字节。</mark></p>
<p>Netty提供一系列实用的编解码器，他们都实现了<code>ChannelInboundHadnler</code>或者<code>ChannelOutboundHandler</code>接口。在这些类中，channelRead方法已经被重写了。<mark>以入站为例，对于每个从入站Channel读取的消息，这个方法会被调用。随后，它将调用由解码器所提供的decode()方法进行解码，并将已经解码的字节转发给ChannelPipeline中的下一个ChannelInboundHandler。</mark></p>
<h3 id="解码器"><a href="#解码器" class="headerlink" title="解码器"></a>解码器</h3><p><strong>ByteToMessageDecoder</strong>   <code>decode()</code>方法进行解码</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123172449318.png" alt="image-20201123172449318"></p>
<p>1)由于不可能知道远程节点是否会一次性发送一个完整的信息，tcp有可能出现粘包拆包的问题，这个类会对入站数据进行缓冲，直到它准备好被处理。</p>
<p>实例</p>
 <figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">ToIntegerDecoder</span> <span class="keyword">extends</span> <span class="title">ByteToMessageDecoder</span> </span>&#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">decode</span><span class="params">(ChannelHandlerContext ctx, ByteBuf in, List&lt;Object&gt; out)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">      	<span class="comment">//判断ByteBuf的字节数是否大于4个字节</span></span><br><span class="line">        <span class="keyword">if</span> (in.readableBytes() &gt;= <span class="number">4</span>) &#123;</span><br><span class="line">            out.add(in.readInt());<span class="comment">//读取Int型数据添加到List中，自动装箱</span></span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>这个例子，每次入站从ByteBuf中读取4字节，将其解码为一个int，然后将它添加到下一个List中。当没有更多元素可以被添加到该List中时，它的内容将会被发送给下一个ChannelInboundHandler。int在被添加到List中时，会被自动装箱为Integer。在调用readInt()方法前必须验证所输入的ByteBuf是否具有足够的数据。</p>
<h3 id="编码器"><a href="#编码器" class="headerlink" title="编码器"></a>编码器</h3><p><strong>MessageToByteEncoder</strong>  <code>Encoder()</code>方法进行编码</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123172403567.png" alt="image-20201123172403567"></p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123173540073.png" alt="image-20201123173540073"></p>
<h2 id="实例"><a href="#实例" class="headerlink" title="实例"></a>实例</h2><p>使用自定义的编码器和解码器来说明Netty的handler 调用机制</p>
<ul>
<li>客户端发送long -&gt; 服务器</li>
<li>服务端发送long -&gt; 客户端</li>
</ul>
<h3 id="服务器"><a href="#服务器" class="headerlink" title="服务器"></a>服务器</h3><p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123202153430.png" alt="image-20201123202153430"></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyServer</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> <span class="keyword">throws</span> InterruptedException </span>&#123;</span><br><span class="line">        NioEventLoopGroup boosGroup = <span class="keyword">new</span> NioEventLoopGroup(<span class="number">1</span>);</span><br><span class="line">        NioEventLoopGroup workerGroup = <span class="keyword">new</span> NioEventLoopGroup(<span class="number">8</span>);</span><br><span class="line"></span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            ServerBootstrap bootstrap = <span class="keyword">new</span> ServerBootstrap();</span><br><span class="line">            bootstrap.group(boosGroup,workerGroup)</span><br><span class="line">                    .channel(NioServerSocketChannel.class)</span><br><span class="line">                    .childHandler(<span class="keyword">new</span> MyServerInitializer());</span><br><span class="line"></span><br><span class="line">            ChannelFuture channelFuture = bootstrap.bind(<span class="number">7000</span>).sync();</span><br><span class="line"></span><br><span class="line">            channelFuture.channel().closeFuture().sync();</span><br><span class="line"></span><br><span class="line">        &#125; <span class="keyword">finally</span> &#123;</span><br><span class="line">            boosGroup.shutdownGracefully();</span><br><span class="line">            workerGroup.shutdownGracefully();</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123202618613.png" alt="image-20201123202618613"></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyServerInitializer</span> <span class="keyword">extends</span> <span class="title">ChannelInitializer</span>&lt;<span class="title">SocketChannel</span>&gt; </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">initChannel</span><span class="params">(SocketChannel ch)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        ChannelPipeline pipeline = ch.pipeline();</span><br><span class="line"></span><br><span class="line">        <span class="comment">//添加入站的handler进行解码 MyByteToLongDecoder</span></span><br><span class="line">        pipeline.addLast(<span class="keyword">new</span> MyByteToLongDecoder());</span><br><span class="line">        <span class="comment">//出站编码</span></span><br><span class="line">        pipeline.addLast(<span class="keyword">new</span> MyLongToByteEncoder());</span><br><span class="line">        <span class="comment">//添加自定义handler</span></span><br><span class="line">        pipeline.addLast(<span class="keyword">new</span> MyServerHandler());</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123203702147.png" alt="image-20201123203702147"></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyServerHandler</span> <span class="keyword">extends</span> <span class="title">SimpleChannelInboundHandler</span>&lt;<span class="title">Long</span>&gt; </span>&#123;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">channelRead0</span><span class="params">(ChannelHandlerContext ctx, Long msg)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;从客户端&quot;</span> + ctx.channel().remoteAddress() + <span class="string">&quot;读取到long&quot;</span> + msg);</span><br><span class="line"></span><br><span class="line">        <span class="comment">//给客户端发送一个long</span></span><br><span class="line">        ctx.writeAndFlush(<span class="number">98765L</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">exceptionCaught</span><span class="params">(ChannelHandlerContext ctx, Throwable cause)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        cause.printStackTrace();</span><br><span class="line">        ctx.close();</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="编码器-1"><a href="#编码器-1" class="headerlink" title="编码器"></a>编码器</h3><p>继承<code>MessageToByteEncoder</code>，重写<code>encode()</code>编码方法</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123204916471.png" alt="image-20201123204916471"></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyLongToByteEncoder</span> <span class="keyword">extends</span> <span class="title">MessageToByteEncoder</span>&lt;<span class="title">Long</span>&gt; </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">//编码方法</span></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">encode</span><span class="params">(ChannelHandlerContext ctx, Long msg, ByteBuf out)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;MessageToByteEncoder encode 被调用&quot;</span>);</span><br><span class="line">        System.out.println(<span class="string">&quot;msg=&quot;</span> + msg);</span><br><span class="line">        out.writeLong(msg);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="解码器-1"><a href="#解码器-1" class="headerlink" title="解码器"></a>解码器</h3><p>继承<code>ByteToMessageDecode</code>，重写<code>decode()</code>解码方法</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123203915543.png" alt="image-20201123203915543"></p>
<p><strong>decode 会根据接受的数据，被调用多次，直到确定没有新的元素被添加到list，或者ByteBuf没有更多到可读字节为止。</strong></p>
<p><strong>如果list out 不为空，就会将list的内容传递给下一个ChannelInBoundHandler处理，该处理器的方法也会被调用多次。</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyByteToLongDecoder</span> <span class="keyword">extends</span> <span class="title">ByteToMessageDecoder</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     *decode 会根据接受的数据，被调用多次，直到确定没有新的元素被添加到list，或者ByteBuf没有更多到可读字节为止。</span></span><br><span class="line"><span class="comment">     * 如果list out 不为空，就会将list的内容传递给下一个ChannelInBoundHandler处理，该处理器的方法也会被调用多次。</span></span><br><span class="line"><span class="comment">     *</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> ctx 上下文对象</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> in  入站的ByteBuf</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> out List集合，将解码后的数据传给下一个handler</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@throws</span> Exception</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">decode</span><span class="params">(ChannelHandlerContext ctx, ByteBuf in, List&lt;Object&gt; out)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line"></span><br><span class="line">        System.out.println(<span class="string">&quot;MyByteToLongDecoder decode 被调用&quot;</span>);</span><br><span class="line">        <span class="comment">//因为long 8个字节,需要判断有8个字节，才能读取一个long</span></span><br><span class="line">        <span class="keyword">if</span> (in.readableBytes()&gt;=<span class="number">8</span>)&#123;</span><br><span class="line">            out.add(in.readLong());</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="客户端"><a href="#客户端" class="headerlink" title="客户端"></a>客户端</h3><p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123203957557.png" alt="image-20201123203957557"></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyClient</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> <span class="keyword">throws</span> InterruptedException </span>&#123;</span><br><span class="line">        NioEventLoopGroup group = <span class="keyword">new</span> NioEventLoopGroup();</span><br><span class="line"></span><br><span class="line">        <span class="keyword">try</span> &#123;</span><br><span class="line">            Bootstrap bootstrap = <span class="keyword">new</span> Bootstrap();</span><br><span class="line">            bootstrap.group(group)</span><br><span class="line">                    .channel(NioSocketChannel.class)</span><br><span class="line">                    .handler(<span class="keyword">new</span> MyClientInitializer());<span class="comment">//自定义初始化类</span></span><br><span class="line"></span><br><span class="line">            ChannelFuture channelFuture = bootstrap.connect(<span class="string">&quot;localhost&quot;</span>, <span class="number">7000</span>).sync();</span><br><span class="line"></span><br><span class="line">            channelFuture.channel().closeFuture().sync();</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">        &#125; <span class="keyword">finally</span> &#123;</span><br><span class="line">            group.shutdownGracefully();</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123204147327.png" alt="image-20201123204147327"></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyClientInitializer</span> <span class="keyword">extends</span> <span class="title">ChannelInitializer</span>&lt;<span class="title">SocketChannel</span>&gt; </span>&#123;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">initChannel</span><span class="params">(SocketChannel ch)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        ChannelPipeline pipeline = ch.pipeline();</span><br><span class="line"></span><br><span class="line">        <span class="comment">//加入一个出站的handler，对数据进行一个编码。</span></span><br><span class="line">        pipeline.addLast(<span class="keyword">new</span> MyLongToByteEncoder());</span><br><span class="line">        <span class="comment">//出站解码</span></span><br><span class="line">        pipeline.addLast(<span class="keyword">new</span> MyByteToLongDecoder());</span><br><span class="line">        <span class="comment">//加入一个自定义对handler，处理业务</span></span><br><span class="line">        pipeline.addLast(<span class="keyword">new</span> MyClientHandler());</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>



<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123202853744.png" alt="image-20201123202853744"></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyClientHandler</span> <span class="keyword">extends</span> <span class="title">SimpleChannelInboundHandler</span>&lt;<span class="title">Long</span>&gt; </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">channelRead0</span><span class="params">(ChannelHandlerContext ctx, Long msg)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;服务器端IP:&quot;</span>+ctx.channel().remoteAddress());</span><br><span class="line">        System.out.println(<span class="string">&quot;收到服务器消息:&quot;</span>+msg);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">channelActive</span><span class="params">(ChannelHandlerContext ctx)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;MyClientHandler 发送数据&quot;</span>);</span><br><span class="line">        ctx.writeAndFlush(<span class="number">123456L</span>);<span class="comment">//发送一个long</span></span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="测试"><a href="#测试" class="headerlink" title="测试"></a>测试</h3><p>我们先来一张图来方便我们分析结果</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/Handler%E8%B0%83%E7%94%A8%E6%9C%BA%E5%88%B6-6137404.png" alt="Handler调用机制"></p>
<p>服务器</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123205645627.png" alt="image-20201123205645627"></p>
<p>(客户端——-&gt;服务器)：入站。服务器接受客户端发送的数据，解码器首先被调用，接着调用我们自定义的ServerHandler打印数据。</p>
<p>(服务器——-&gt;客户端)：出站。服务器发送数据给客户端首先调用我们自定义的处理器ServerHandler，接着调用编码器，打印数据。</p>
<p>客户端</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123205713335.png" alt="image-20201123205713335"></p>
<p>(客户端——-&gt;服务器)：出站。客户端一启动首先调用我们自己编写的ClientHandler发送数据，接着调用编码器编码数据。</p>
<p>(服务器——-&gt;客户端)：入站。首先使用解码器解码服务器发送的数据，接着传递调用给自定义的ClientHandler。</p>
<p>测试结果与分析结果一致测试成功！</p>
<h3 id="细节"><a href="#细节" class="headerlink" title="细节"></a>细节</h3><p>我们修改客户端发送的数据为一个16字节的字符串按UTF-8编码。运行测试。</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123213136422.png" alt="image-20201123213136422"></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyClientHandler</span> <span class="keyword">extends</span> <span class="title">SimpleChannelInboundHandler</span>&lt;<span class="title">Long</span>&gt; </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">channelRead0</span><span class="params">(ChannelHandlerContext ctx, Long msg)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;服务器端IP:&quot;</span>+ctx.channel().remoteAddress());</span><br><span class="line">        System.out.println(<span class="string">&quot;收到服务器消息:&quot;</span>+msg);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">channelActive</span><span class="params">(ChannelHandlerContext ctx)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        System.out.println(<span class="string">&quot;MyClientHandler 发送数据&quot;</span>);</span><br><span class="line">        <span class="comment">//ctx.writeAndFlush(123456L);//发送一个long</span></span><br><span class="line"></span><br><span class="line">        <span class="comment">//1.&quot;abcdabcdabcdabcd&quot; 是16个字节</span></span><br><span class="line">        <span class="comment">//2.该处理器的前一个handler是MyLongToByteEncoder没有进行编码处理 为什么？原因在它的父类 MessageToByteEncoder</span></span><br><span class="line">        <span class="comment">//因此我们编写 Encoder 是注意传人的数据类型和处理的数据类型一致</span></span><br><span class="line">        ctx.writeAndFlush(Unpooled.copiedBuffer(<span class="string">&quot;abcdabcdabcdabcd&quot;</span>, CharsetUtil.UTF_8));</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123213307154.png" alt="image-20201123213307154"></p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123213427984.png" alt="image-20201123213427984"></p>
<p>16字节每次只读Long类型也就是8字节，所以需要读两次。每次解码过后就交给了ServerHandler处理，也就发送了<code>98765L</code>从而也调用了两次编码器。</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123213626062.png" alt="image-20201123213626062"></p>
<p>发送字符串数据没有调用Long类型编码器的编码方法。</p>
<p>后面是接受服务器两次发送的数据流程。</p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/image-20201123213724130.png" alt="image-20201123213724130"></p>
<p><img src= "https://gitee.com/kylincw/images/raw/master/loading.gif" data-lazy-src="https://qiniu.codekylin.cn/img/Handler%E5%A4%84%E7%90%86%E7%BB%86%E8%8A%82.png" alt="Handler处理细节"></p>
<p>不论解码器handler 还是 编码器handler 即接收的消息类型必须与待处理的消息类型一致，否则该handler不会执行相应操作。</p>
<p>在解码器 进行数据解码时，需要判断缓存区(ByteBuf)的数据是否足够 ，否则接收到的结果会期望结果可能不一致</p>
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